1. Field of the Invention
The present invention relates to the delivery of content over a broadcast network, particularly although not exclusively a broadband digital broadcast network.
2. Description of the Prior Art
Broadband digital broadcast networks are known in which video and audio data are transmitted to a users equipped with suitable receivers. One such well known network is the terrestrial Digital Video Broadcasting (DVB-T) system found in Europe and elsewhere where the video and audio data comprises a plurality of channels allowing the user to select from a range of content. It has also been proposed to utilize such networks not only for the transmission of video and audio data but also for the delivery of more general data types including TCP/IP data traffic.
The delivery of more general data types such IP data as may differ from the typical delivery of video and audio data in that rather than the network operator providing the same content to all users (broadcast), a specific user (unicast) or group of users (multicast) may require specific content. In order to deal with such a range or transmission scenarios, the addressing of content using conditional access has been proposed. Conditional access adds a unique, usually encrypted, identifier to content such that only a receiving terminal with the relevant decryption capability can receive the content.
Further details of Conditional Access in relation to DVB can be found in the following ETSI Publications DVB-CI Common Interface Specification for Conditional Access and other Digital Video Broadcasting Decoder Applications EN50221 (V1:02/97) and Guidelines for Implementation and Use of the Common Interface for DVB Decoder Applications R 206 001 (V1: 1998) A025 (5/97).
However, although conditional access allow the addressing of an individual terminal or, indeed a group of terminals, it nevertheless remains necessary to transmit content using all the transmitters in the network irrespective of whether the content is included in a broadcast, multicast, or unicast.